In conventional manner, such a terminal includes a camera having a lens system, a monitor display screen, manual or automatic control means, and an electronic assembly for the purposes of control, coding/decoding, and interfacing with a transmission line.
The above set of equipment is housed in a box or case which is generally intended to be positioned on a table at which the speaker is sitting, but numerous other forms of support may be envisaged.
However, the image obtained by the camera of such a terminal suffers from a major drawback: given that both in daylight and under artificial lighting, ambient illumination generally comes from above the subject, the resulting image picked up by the camera suffers from very marked shadows, particularly on a speaker's face, and most particularly beneath the eyes. These shadows are unattractive, and this effect is further accentuated by the fact that image resolution is limited to about 150.times.200 pixels on low data rate lines.
A videophone-type terminal including its own light source has already been described in the prior art, for example in European Patent Application No. 0 231 403, in French Patent No. 914,843, and in U.S. Pat. No. 4,485,400. However, none of the terminals in these patents is suitable for compensating image defects due to overhead ambient illumination.
The present invention seeks to mitigate this drawback of the prior art and to provide a terminal of the above-specified type suitable for obtaining relatively uniform lighting over the face of the user, and thereby obtaining improved image quality.